Ga-68 DOTATATE Positron Emission Tomography-Computed Tomography Imaging in Oncogenic Osteomalacia: Experience from a Tertiary Level Hospital in South India

Sinonasal phosphaturic mesenchymal tumour: radiation oncologist's perspective

Tumour-induced osteomalacia is a rare cause of osteomalacia, the majority of which is of mesenchymal origin. Oncogenic osteomalacia is a potentially curable condition caused by phosphaturic mesenchymal tumours. We present the case of a woman in her 30s with a sinonasal phosphaturic mesenchymal tumour, treated with surgical excision followed by adjuvant intensity-modulated radiotherapy and subsequent adjuvant chemotherapy. The patient experienced minimal adverse effects during radiation. There was good local control and cosmetic outcomes with no radiation-related toxicity at a follow-up period of 32 months.

Clinical Applications of Somatostatin Receptor (Agonist) PET Tracers beyond Neuroendocrine Tumors

Somatostatin receptor (SSTR) agonist tracers used in nuclear medicine scans are classically used for neuroendocrine tumor diagnosis and staging. SSTR are however, expressed more widely in a variety of cells as seen in the distribution of physiological tracer uptake during whole body scans. This provides opportunities for using these tracers for applications other than NETs and meningiomas. In this qualitative systematic review, novel diagnostics in SSTR-PET imaging are reviewed. A total of 70 studies comprised of 543 patients were qualitatively reviewed. Sarcoidosis, atherosclerosis and phosphaturic mesenchymal tumors represent the most studied applications currently with promising results. Other applications remain in progress where there are many case reports but a relative dearth of cohort studies. [¹⁸F]FDG PET provides the main comparative method in many cases but represents a well-established general PET technique that may be difficult to replace, without prospective clinical studies.

Extended Whole-body Ga-68 DOTATATE PET-CT in evaluating Tumour-Induced Osteomalacia: Case report and review of literature

Tumour-induced osteomalacia is a rare paraneoplastic syndrome that manifests as chronic hypophosphataemia, non-specific bone pain and muscle weakness. It is generally caused by phosphaturic mesenchymal tumour (PMT), which is uncommonly associated with synchronous tumours. However, diagnosis is often delayed for several years due to the rarity, indolent growing nature and non-specific symptoms of the disease, often resulting in an overlook by clinicians during assessments. The patient initially presented with hypophosphataemia and generalised skeletal pain with multiple atraumatic fractures. Blood tests revealed serum calcium levels at the upper limit and extremely low inorganic phosphate levels. Herein, we report a case where two synchronous PMTs from two different sites were detected by 'extended' whole-body Ga-68 DOTATATE PET-CT, leading to remission of the disease after complete surgical removal. Early detection and diagnosis of PMT neoplasm is crucial, as complete surgical resection of this tumour is the only definitive treatment currently known. Upon excision, this curable disease will result in complete resolution of symptoms and blood parameters, leading to remission of the disease which significantly improves the patient's quality of life. PMT often over-expresses somatostatin receptors (SSTR), predominantly subtype 2A, and Ga-68 DOTATATE PET-CT is a selective SSTR imaging that targets this characteristic over-expression in these tumours. The high diagnostic accuracy of Ga-68 DOTATATE PET-CT should be the primary imaging modality for full evaluation of this disease.

Diagnostic utility of Ga-68 DOTA-SSTR and F-18 FDG PET/CT in the detection of culprit tumours causing osteomalacia: a systematic review and meta-analysis

BACKGROUND

Tumour-induced osteomalacia (TIO) or oncogenic osteomalacia is a rare variant of paraneoplastic syndrome secondary to a small benign phosphaturic mesenchymal tumour that secretes phosphaturic substances. Complete tumour excision is often curative. However, the localization of these offending tumours has always remained a challenge because of their small size, slow-growing nature, and presence in atypical locations. We performed a systemic review and meta-analysis on the sensitivity and specificity of F-18 FDG PET/CT and Ga-68 DOTA-SSTR PET/CT to detect tumours causing osteomalacia.

METHODS

Pub Med, SCOPUS, the Cochrane Library and Web of Science were searched for articles on F-18 FDG and Ga-68 DOTA-SSTR PET/CT in the detection of culprit tumours in TIO till September 2020. Both retrospective and prospective studies having three or more patients were included. The methodological quality of included studies was assessed using the Revised Tool for the Quality Assessment of Diagnostic Accuracy Studies-2 checklist. A random-effect model was used for the statistical pooling of sensitivity and specificity. Pooled data were presented with 95% confidence intervals (95% CI) and displayed using Forest plots. Heterogeneity was expressed using the I2 statistic.

RESULTS

The pooled sensitivity of Ga-68 DOTA-SSTR PET/CT in detecting the culprit tumour derived from all included studies is 86% (95% CI: 79-91%). There is moderate statistical heterogeneity among the included studies (I2 = 72.7%). The pooled sensitivity of F-18 FDG PET/CT in detecting the offending tumour derived from all included studies is 73% (95% CI: 61-84%) with moderate statistical heterogeneity among the included studies (I2 = 45.4%).

CONCLUSION

In the detection of offending tumours in TIO, Ga-68 DOTA-SSTR PET/CT has better sensitivity than F-18 FDG PET/CT and should be used as first-line imaging modality due to very high sensitivity.

Diagnostic efficiency of 68Ga-DOTANOC PET/CT in patients with suspected tumour-induced osteomalacia

OBJECTIVES

Currently, the main challenge in tumour-induced osteomalacia (TIO) is the difficulty in locating culprit tumours for definitive diagnosis and surgical therapy. Herein, we retrospectively evaluate the efficiency of ⁶⁸Ga-DOTANOC PET/CT in the localisation and diagnosis of TIO, and compared with ¹⁸F-FDG.

METHODS

Twenty-four consecutive patients with hypophosphataemic osteomalacia (HO) and suspicion of TIO who were referred to our centre for ⁶⁸Ga-DOTANOC PET/CT scanning were retrospectively reviewed. The images were evaluated qualitatively as well as semi-quantitatively, and imaging results were compared with the final diagnoses.

RESULTS

Among the total of 21 patients who were included in the final analyses, 17 were diagnosed with TIO, while four were proven to have other causes of HO. ⁶⁸Ga-DOTANOC PET/CT produced positive results in 16 of the 17 patients with TIO, representing a sensitivity of 94.1%. Moreover, the ⁶⁸Ga-DOTANOC PET/CT results were negative in 3 of the 4 patients without TIO, representing a specificity of 75.0%. The overall accuracy of ⁶⁸Ga-DOTANOC PET/CT in locating the tumours responsible for TIO is 90.5%. In particular, ⁶⁸Ga-DOTANOC PET/CT detected the culprit tumours in 4 out of 10 patients with negative results on previous ¹⁸F-FDG PET/CT and showed a significantly higher T/M ratio of tumours than ¹⁸F-FDG PET/CT in the same patients (n = 10; 4.76 ± 3.08 vs 1.95 ± 1.33, p < 0.05).

CONCLUSIONS

⁶⁸Ga-DOTANOC PET/CT is an accurate imaging modality in the localisation of tumours for TIO. It is superior to ¹⁸F-FDG PET/CT and may be useful in the differential diagnosis of HO.

KEY POINTS

• TIO should be considered a possible cause for patients diagnosed with HO, which usually needs to be differentiated from other aetiologies. • ⁶⁸Ga-DOTANOC PET/CT is an accurate imaging modality in locating culprit tumours for TIO, superior to ¹⁸F-FDG PET/CT.

Detection Rate of Culprit Tumors Causing Osteomalacia Using Somatostatin Receptor PET/CT: Systematic Review and Meta-Analysis

Background: Tumor-induced or oncogenic osteomalacia (TIO) is a rare paraneoplastic syndrome in which osteomalacia is a consequence of fibroblast growth factor 23 (FGF23) secretion by a mesenchymal tumor. The localization of the culprit lesion in patients with TIO is often challenging. Several studies have evaluated the detection rate (DR) of these tumors using somatostatin receptor positron emission tomography (SSTR-PET/CT). We aimed to summarize literature findings on this topic providing pooled estimates of DR. Methods: A comprehensive literature search by screening PubMed, Embase and Cochrane library electronic databases through August 2019 was performed. The pooled DR of culprit tumors using SSTR-PET/CT in patients with TIO was calculated using a random-effects statistical model. Results: Fourteen studies on the use of SSTR-PET/CT in detecting the culprit tumor in patients with TIO were included in the qualitative analysis. The pooled DR of SSTR-PET/CT on a per-patient-based analysis calculated using eleven studies (166 patients) was 87.6% (95% confidence interval (95% CI) 80.2–95.1%). Statistical heterogeneity among studies was detected (I-square = 63%), likely due to the use of different radiolabeled somatostatin analogues, as demonstrated by a subgroup analysis. Conclusions: Despite limited literature data due to the rarity of the disease, SSTR-PET/CT demonstrated a very high DR of culprit tumors in patients with TIO and it could be used as first-line imaging method for this indication.